Discharges of hazardous organic compounds into the environment have led to contamination of surface water, soil, and aquifers resulting in potential public health problems and degradation of the land for future use. As used in this specification and appended claims, hazardous organic compound means a chemical or substance that is either toxic or highly toxic, an irritant, corrosive, a strong oxidizer, a strong reducer, a strong sensitizer, combustible, either flammable or extremely flammable, dangerously reactive, pyrophoric, pressure-generating, a compressed gas, a carcinogen, a teratogen, a mutagen, a reproductive toxic agent, or is suspected of having adverse health effects on humans. In many cases, subsurface groundwater contaminant plumes may extend hundreds to thousands of feet from the source area of a chemical release resulting in extensive contamination. These chemical contaminants may then be transported into drinking water sources, lakes, rivers, and even basements of homes.
The U.S. Environmental Protection Agency (USEPA) has established maximum concentration limits (MCL's) for various hazardous organic and inorganic compounds in water and soils. For instance, stringent drinking water limits placed on many solvent organic compounds in water can be as low as 0.005 mg/L (parts per billion).
The presence of hazardous compounds in subsurface soils, surface water, and groundwater is a well-documented and extensive problem. The source of these hazardous materials is often times from industry where the materials are released onto the soil surface or surface water or even into the subsurface soil and/or groundwater through leaking storage tanks. Many, if not most, of these compounds are capable of moving through the soil under the influence of moving water, gravity, or capillary action and serve as a source of groundwater contamination. As used in this specification and appended claims, soil is to be interpreted broadly to include all naturally occurring material found below ground surface (e.g. silts, clays, sands, rock, karsts, organics, tills, etc.).
Soil, surface water, groundwater, and wastewater can become contaminated by a variety of substances. The substances include, without limitation, metals, volatile, semi-volatile, and non-volatile organic compounds. Common examples of such contaminates include arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver, PCBs, gasoline, oils, wood preservative wastes, and other hazardous organic compounds. Such other hazardous organic compounds may include, but not limited to, chlorinated solvents (such as trichloroethylene (TCE), vinyl chloride, tetrachloroethylene (PCE), and dichloroethanes), ethylene dibromide, halobenzenes, polychlorinated biphenyls, acetone, ter-butyl alcohol, tert-butyl formate, and anilines. Additional contaminants include compounds containing at least one oxidizable aliphatic or aromatic compound and/or functional group (e.g. atrazine, benzene, butyl mercaptan, chlorobenzene, chloroethylvinyl ether, chloromethyl methyl ether, chlorophenol, chrysene, cyanide ion or organic cyanides, dichlorophenol, dichlorobenzene, dichloroethane, dichloroethene, dichloropropane, dichloropropene, ethyl alcohol, ethylbenzene, ethylene glycol, ethyl mercaptan, hydrogen sulfide, isopropyl alcohol, Lindane™, methylene chloride, methyl tert-butyl ether, naphthalene, nitrobenzene, nitrophenol, pentachlorophenol, phenanthrene, phenol, propylene, propylene glycol, Silvex™, Simazine™, sodium sulfide, tetrachloroethane, tetrachloroethene, toluene, trichlorobenzene, trichloroethane, trichloroethene, trichlorophenol, vinyl chloride, xylene, etc).
Contaminated soil and groundwater must be removed or treated to make it less toxic and to meet USEPA requirements. There are a variety of reactants and methods for treating contaminated soil, surface water, groundwater, and wastewater as discussed below.
Peroxydisulfate's have been reported as applied constituents for organic carbon digestion or decomposition. Application methods include thermally activated persulfate oxidation in conjunction with an electro-osmosis system to heat and transport persulfate anions into soils.
Permanganate(s) and peroxygen(s) reactant(s) have also been reported as applied constituents for oxidation of organic compounds. Peroxygen compound(s) applied independently or in conjunction with a metallic salt catalyst(s) (complexed and not complexed; chelated and not chelated) have been shown to break down organic compounds within the soil, groundwater, and wastewater.
Groundwater and subsurface soil typically has been treated by injecting reactant(s), with or without a catalyst(s), within an aqueous mixture, slurry, or suspension into the subsurface. Injection into the subsurface is accomplished by gravity feed or the use of a pump(s) to increase well head pressure. This results in the subsurface dispersion of the reactant(s) within the area of the injection well.
Another method for in situ treatment of groundwater includes the excavation of a trench proximate or downstream of a subsurface plume of organic and/or inorganic contaminant(s). The trench is filled with reactant(s) and a permeable media(s) (i.e. sand) for the plume to flow through, subsequently reacting oxidizable and/or reducable organic and/or inorganic compounds that come into contact with the reactant(s). These trenches filled with a reactant are often referred to as permeable reactive barriers (PRBs). One limiting factor in current methods of installing PRBs is that structures, roads, or other improvements to the land above the installation site may need to be destroyed when digging the trench. Alternatively, the trench may need to be located further down flow of the plume of contamination than desired, to avoid destruction of improvements to the land nearer the plume of contamination. Other limiting factors may include a requirement for heavy equipment and the need to move the heavy equipment across the land to excavate the trench which may be destructive or detrimental to the ground. Additionally, current methods for installing PRBs may require disposal of large volumes of cuttings or soils removed to form a trench. These removed cuttings or soils may be hazardous which may increase health and safety requirements and disposal costs.
The methods used for ex situ treatment or in situ treatment of surface contamination, water or soil, typically involve the direct application of the reactant(s) to the hazardous organic compound(s). In the case of ex situ surface soil treatment, the soil is often times mixed or tilled to ensure contact of the reactant(s) with the hazardous organic compound(s).
Meeting USEPA cleanup criteria with these reactants and methods of the prior art has been found to be difficult, costly, and even impossible. With some of these current methods and reactants, there has been questionable showing that their application results in the effective or efficient removal of contaminants.
Current methods involving the use of peroxide group(s) (i.e. hydrogen peroxide) in conjunction with iron salt catalyst(s) have shown to be relatively inefficient, often resulting in incomplete contaminant oxidation. Hydrogen peroxide in particular has been found to lack persistence in contaminated soils and groundwater due to rapid dissociation. Many of these current employed reactants are hazardous and difficult to handle.
Recently, the use of permanganate(s) has been found to be an effective oxidizing agent of certain hazardous organic compound(s). However, known methods to use that ability to actually remediate a site requires exceedingly large quantities of permanganate(s) to overcome the natural oxidant demand exerted by the soil, thereby limiting the percentage available for oxidizing the hazardous organic compound(s). Large amounts of permanganate(s) may thus be required per unit of soil and groundwater volume, limiting the application of this technology due to high cost. Additionally, a product of the permanganate(s) oxidation reaction is solid manganese dioxide, which may precipitate and clog the soil or aquifer, resulting in a reduced permeability of the soil to water. This clogging may reduce the hydraulic conductivity of the soil and thereby inhibit oxidant access to the entire contaminated site, rendering treatment of the soil and the groundwater plume flowing therethrough, incomplete.
Because of these limitations of the art before the present invention, there is a need for improved methods of insitu treatment of soil and groundwater contamination.